Group_J___ASTRONOMY_LAB_2.pdf

AST2002L Discovering Astronomy Lab Lab #2 Observing the Sky List the names of all participating team members for this lab. _______Kobe Rosenberg______ _________Esther Gasent_______ ____José Riquelme Orgilés_____ ______Aberto Vento Marco_____ Big Idea: Objects in the sky have properties, locations, and predictable patterns of movements that can be observed and described. Those motions explain such phenomena as the day, the year, the seasons, phases of the Moon, and eclipses. In this lab you will conduct a series of inquiries about the motion of objects in the sky using sky simulation software and learn about the Altitude-Azimuth and Right Ascension-Declination coordinate systems that astronomers developed to help locate objects in the sky. By becoming familiar with the sky and its motions you should become more able to locate and identify celestial objects. Lab Equipment: ● Stellarium, a free planetarium program at: stellarium-web.org

Part 1. Exploring the night sky Instead of the real night sky, this lab uses the planetarium program Stellarium to allow you to visualize the locations and motions of celestial objects observed from any place and time on Earth. You can move forward and backward in time and easily view how the sky changes over periods of a few minutes to hundreds or thousands of years. Open Stellarium and you should find yourself facing North, about an hour after sunset. To move the sky, click and drag a part of the night sky. To zoom in and out, use the mouse scroll wheel. Toggle on the Constellations on the control bar along the bottom. The control bar looks like this: 1. Locate the constellation Ursa Major. Describe where it is in the sky just after sunset tonight. How will it move as the night passes? As the Earth rotates, the Ursa Major and its neighbor in the sky, the Ursa Minor, revolve around the North Star. From the Northern Hemisphere, both are in the sky continuously, always on their horizon, circling endlessly around the so-called Polaris (Pole Star). Its Azimuth is 031°29'01.6" and its Altitude is +11°59'51.6" at the time of the sunset. Constellations are helpful for "naked eye" observations, but astronomers often need to be more precise in describing a particular object’s position on the sky. The Altitude-Azimuth coordinate system places an object with respect to your local horizon. Altitude (Alt) is measured up from the horizon to the object, with 0 the horizon and 90 the zenithAzimuth. (Az) is a ̊ ̊ more precise measure of compass direction. Imagine a line drawn directly over your head (the zenith) connecting north and south. Azimuth measures where your imaginary line meets the horizon as degrees eastward from North. In Stellarium, you can view the lines of altitude and azimuth by toggling the Azimuthal Grid on the bottom control bar. 2. Using Stellarium, complete the table below as viewed from your location at ~9 PM tonight: Altitude (°) Azimuth (°) Constellation Vega 343°44'49.5" -18°28'46.9" Northern constellation of Lyra

have used the stars as a guide for millenia. Toggle off the Azimuthal Grid and turn on the Equatorial Grid. At the center of the Equatorial grid lines is a not-very-bright star in the handle of Ursa Minor (the Little Dipper). This star is Polaris. To find out if you have correctly identified Polaris, click on the star. A window will pop up with the star's name and information about it. 5. Measure the altitude of Polaris (the angle from the horizon up to the star) rounded to the nearest degree, and enter this value in the table below for Jacksonville. Make sure that you recording the altitude and NOT the azimuth. Next choose 6 different locations on Earth and use Stellarium to measure the altitude of Polaris at each location. Pick 3 locations in the northern hemisphere and 3 locations in the southern hemisphere. To change your location click where it says JACKSONVILLE (or a location) in the lower left of the display and turn off Autolocation. You can then search for locations or just move the blue location marker. Enter Latitude and Longitude as numbers in degrees. The convention is that negative Latitudes are South and negative Longitudes are West. Altitudes should be positive if the star is above the horizon and negative if the star is below. Make sure to record the altitude even if Polaris is below the horizon. Location Latitude (°) Longitude (°) Altitude of Polaris (°) UNF 30.3007 -81.4421 +30°52' 21.4’’ Valencia 39.46971 -0.37634 +39°19'10.5’’ Paris 48.85889 2.32004 +48°40'11.6’’ Quebec 46.81374 -71.20841 +47°20'30.8’’ Rosario -32.95950 -60.66154 -32°30'57.9’’ Cape Town -33.92899 18.41740 -34°17'28.8’’ Sydney -33.86984 151.20828 -33°24'56.2’’ 6. Sketch graphs of “Polaris Altitude versus Latitude” and “Polaris Altitude versus Longitude,” also called scatter plots or correlation plots. You may use a spreadsheet such as Excel or Google Sheets if you like.

7. In your plots, what if any patterns can you identify for possible relationships between the altitude of Polaris and the longitude and latitude of the observer? Explain your reasoning and provide evidence to support your conclusion. If you feel you need to collect additional data to determine whether or not there is a correlation, please do so, adding the points to your graphs above. Vertically above at the North Pole is Polaris. Or it makes a 90° angle above the horizon at that location, which corresponds to the North Pole's latitude. The reason for this is that, from the North Pole, Polaris seems to be directly overhead. It appears to be at a 90-degree. It starts to appear "lower" in the night sky as you move south. Then, the star would appear to be 45 degrees (altitude) above the horizon when you are 45 degrees north (latitude). As a result, the latitude of any location on Earth is equal to the angle of Polaris above the horizon at that location. (altitude of Polaris is almost the same as the latitude of where the observer is). 8. Sketch a diagram showing the Earth, Polaris, and an observer in the N. Hemisphere of the Earth. Explain why Polaris is useful for navigators, making reference to your sketch. Nowadays technology has advanced exponentially and there are multiple tools to navigate or locate like satellites, GPS, and compasses... Nevertheless, in the past navigators relied on a star and this star was called Polaris. Since Polaris remains stationary in the sky, just above the Earth's rotation axis, it always points north, regardless of its rotation. We know Polaris for its

11. A fellow student proposes the following generalization: “Sunset time changes by about one hour per month, setting earlier and earlier in the fall and then setting later and later in the spring.” Based on the evidence you’ve collected in this section, do you agree or disagree with that statement? Explain your reasoning and provide evidence either from the table above or from additional evidence you yourself generate using Stellarium. This statement is correct because during the fall the Sun sets in about one hour before every month and in the Spring the Sun sets in about one hour later. However, in the months of December, January, February and March, the Sun sets later every month but just a few minutes. This can be well explained in the following graph: 12. Consider the statement, “The Sun sets more towards the south in winter months and more towards the north in summer months, as observed from Jacksonville.” Based on the evidence you’ve collected, would you agree or disagree with this generalization? When explaining your reasoning, provide specific evidence that you yourself collected. On an azimuth circle, an azimuth is a direction that is measured in degrees clockwise from north. Azimuth circles have 360 degrees on them. East is represented by 90 degrees, south by 180 degrees, west by 270 degrees, and north by 0 degrees and 360 degrees. As can be seen, in Winter the Azimuth degrees are much lower and closer to 180 ° than in Summer. This indicates that the Sun sets more towards the South in Winter than in Summer which is more towards the North. In conclusion, the statement is correct.

Part 3: Motion of the Sun Against the Stars Now, we can introduce a second coordinate system in which stars have “fixed” positions on the sky. Right Ascension-Declination is similar to the longitude and latitude coordinates that define positions on the surface of Earth. Extending the Earth’s Equator out into space creates the Celestial Equator. Celestial ‘latitude’, the number of degrees a star or celestial object is above or below the Celestial Equator, is called Declination or Dec. Celestial ‘longitude’ is called Right Ascension or R.A. and increases and decreases along the Celestial Equator. In astronomy, R.A. is not measured in units of degrees, but in units of hours. By convention, an R.A. of 0 hours corresponds to the point in the sky where the Sun crosses the Celestial Equator on the first day of Spring in March, and increases going eastward. Because one Earth day is 24 hours, an R.A. of 24 h is the same as an R.A. of 0 h . This can sound complicated at first, but the main advantage of the R.A. and Dec system is that it tells you the fixed position of a star and is the same for every observer on Earth, whereas Altitude and Azimuth change with an observer’s location, the time of night and the time of year. 13. The entire Celestial Equator extends over 24 hours of Right Ascension. There are 360 in ̊ a circle. How many degrees are in one hour of R.A.? Show your work. Right ascension is measured in hours so, to get the degrees that are in an hour. We should establish the following relation: if 24 hours is 360 °, then, how many degrees are in 1 hour? 24 hours = 360° 1 hour = x° So, 360°/24h = 15° are in one hour of R.A. 14. Locate the Sun with respect to the “fixed” stars of the right ascension and declination coordinate system. Set Stellarium to noon today. Toggle the Atmosphere off and pause the rotation of the sky. In which constellation is the Sun? As we can appreciate in the following screenshot of Stellarium, the Sun is in Capricornus’ constellation.

18. From your answer to the previous questions, what general statement can you make about how the Sun and stars appear to move together through the sky over the course of the day (24 hours)? Be sure to provide evidence for your conclusion. In the same way that the Earth rotates each day, so do the stars, which revolve around the celestial pole. Furthermore, constellations change over the course of the year due to the Earth's rotation around the Sun. In the course of the Earth's rotation, the stars rise on the eastern horizon and set on the western one. While the Earth rotates, it appears that the sky revolves around the two celestial poles. As the stars rise and set along the horizon, their circumferences will trace parallel lines. 19. Return to noon today. For the times listed in the table below, find the constellation of stars closest to the Sun, and record the R.A. and Dec. of the Sun. Time from Date Constellation R.A. Dec. today at noon 0 days (noon 02/01/2023 Capricornus 21h 00m06.1s -17°02'16.1" today) One day 02/02/2023 Capricornus 21h 04m10.1s -16°44'59.2" One week 02/08/2023 Capricornus 21h 28m17.1 -14°55'24.6" Two weeks 02/15/2023 Aquarius 21h 55m50.1s -12°36'12.7" Three weeks 02/22/2023 Aquarius 22h 22m48.6s -10°06'58.9" One month 03/01/2023 Aquarius 22h 49m16.3s -07°30'11.0" Two months 04/01/2023 Pisces 00h 42m54.1s +04°36'41.5" Three months 05/01/2023 Cetus/Aries 02h 34m24.8s +15°08'06.2" Five months 07/01/2023 Gemini 06h 41m41.5s +23°05'31.0" Seven months 09/01/2023 Leo 10h 42m16.5s +08°12'23.3" Nine months 11/01/2023 Libra/Virgo 14h 26m18.4s -14°29'11.5" One year 02/01/2024 Capricornus 20h 59m07.4s -17°06'23.5" Two years 02/01/2025 Capricornus 21h 02m13.5s -16°53'19.0" 20. Consider the research question, "In which direction does the Sun move compared to the background constellations?" What conclusions and generalizations can you make by

analyzing the patterns in the data you have collected? Explain your reasoning and provide evidence that you collected to support your conclusion. Over a year, the Sun appears to drift eastward with respect to the stars. In 365.24 days, it completes one full rotation of 360 degrees. In its orbit around the Sun, the Earth drifts eastward due to its motion around the Sun. Sun rises in the eastern sky, rises towards the equatorial direction before lowering down and setting in the western sky. The constellations, however, tend to shift westward over time if observed through the year. The reason for this is the Earth's orbit around the Sun. During the summer, viewers look at space in a different direction than they do during the winter. 21. For the times that you have recorded in your table, mark the position of the Sun on the empty plot of right ascension versus declination below. 22. What conclusions and generalizations can you make from the specific path of the Sun through the constellations throughout the year? (This path is called the ecliptic.) Explain your reasoning and provide evidence to support your conclusion. The ecliptic describes the linear path the Sun follows across the sky. It extends a few degrees above and below the ecliptic line and is composed of constellations called the zodiac. An ecliptic is a line that describes the plane of Earth's orbit around the Sun. The apparent position of the Sun makes a complete circuit of the ecliptic in one year because Earth orbits the Sun once a year. The Sun moves slightly less than 1° eastward every day in a year with slightly more than 365 days. During the course of a year, the sun passes

Part 4: What Evidence Do You Need to Pursue a Question? 23. Consider the tweet above. Create a detailed, step-by-step description of the evidence you would need to collect using Stellarium to prove or disprove the above statement. You must include a table and sketches – the goal is to be precise and detailed enough that someone else could follow your procedure. One statement that could be correct is that when summer arrives, the days are longer and this can be verified by observing the average number of hours of sunshine on summer days and comparing it with the rest of the seasons. What would not be correct is the statement referred to in the tweet insinuating that throughout the summer the days are getting longer, that would be incorrect. Since as Tyson says, the longest day of the year is the first day of summer and from this onwards the length of sunshine hours during this season is reduced. We can prove this by analyzing the history of the duration of each day of the summer. Using Stellarium we can see at what time the sun rose and set each day. To prove whether the tweet's statement is correct or not, by performing a simple experiment in which we take the sunrise and sunset times of the summer season we can demonstrate whether it is true or not. 1. We have to choose one place on Earth. In this case I will choose Jacksonville. 2. We chose a reference year, in this case 2022. 3. Then we calculate, using the information obtained with Stellarium, the daylight hours of three key days of that summer: The first, the middle and the last one (June 21, August 7 & September 22; to make the experiment simple, although it would be optimal to take these measurements every day of the summer). To make this calculation, we must look at the exact time of day when Stellarium announces the change between Dawn-Daylight and Daylight-Twilight: 1st day of summer 2022 in Jacksonville (June 21): 14h 29min between Sunrise and Sunset Sunrise at 6:15 a.m. Sunset at 8:39 p.m.

Mid-summer 2022 in Jacksonville (August 7): 13h 55min Sunrise at 6:44 a.m. Sunset at 8:39 p.m. Last day of summer 2022 in Jacksonville (September 22): 12h Sunrise at 7:12 a.m. Sunset at 7:12 p.m. By performing this experiment we can observe that, as Neil deGrasse Tyson states, the first day of summer is the day with more sunlight (longer), and as the summer progresses, the days have fewer hours of daylight (shorter). We can affirm that Tyson's statement is correct. P.S: To increase the reliability of our experiment we could take these measurements and perform it in the same way but taking all the days of the summer, in several years and in different places on Earth.

8/21/2022 13hr 6min -44min 9/21/2022 12hr 10min -56min 10/21/2022 11hr 16min -54min 11/21/2022 10hr 29min -47min 12/21/2022 10hr 9min -10min Performing my colleague's experiment, I consider that we can also affirm that, as well stated in the tweet, the first day of summer is the longest day of the year and during the rest of the summer the days are continuously getting shorter and shorter (less hours of sunlight). However, it could have been more accurate without taking so much information since what we have to analyze in the experiment is not the duration of all the days of the year but of the days of the summer season.

25. Treating Tyson’s tweet as a research statement, write an evidence-based conclusion about the change in the length of days in summer. Be sure to refer to the evidence that you collected. If we treat Tyson's tweet as a research claim we must look for the evidence that shows us what exactly happens to the length of days throughout the summer and why this is so. This can be done very simply by referring to the phases of the Earth's translation around the Sun. The evidence on which I am going to base myself are the information we have about this path and we know that there are 4 phases differentiated in summer and winter solstices and spring and autumn equinoxes. And as we have been able to demonstrate with our experiments and also with all the resources we have at our disposal, the summer solstice is the peak day in terms of sunlight hours and the winter solstice is the valley day in terms of daylight hours. This is enough evidence to affirm that, between the winter solstice and the summer solstice, passing through the spring equinox, the number of hours of sunlight increases. Once the summer solstice arrives, it will be the day with more daylight hours of the year, and again until the winter solstice but passing through the autumn equinox, the number of sunlight hours of each day will be reduced.